Vehicle monitoring method, specific character pattern recognition device, and vehicle monitoring system

ABSTRACT

In a vehicle monitoring method, recognition processing of a specific character pattern of a vehicle is performed by extracting a specific character pattern area from a taken image data. When the specific character pattern cannot be recognized, a compression range is judged as being a vehicle area clipped from the taken image data, and image data of the clipped area is compressed at a low compression ratio. When the specific character pattern is partially recognized, the compression range is judged as being the specific character pattern area clipped from the taken image data, and image data of the clipped area is compressed at the low compression ratio. When the specific character pattern is fully recognized, the compression range is judged as being the specific character pattern area clipped from the taken image data, and image data of the clipped area is compressed at a high compression ratio.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority ofJapanese Patent Application No. 2005-012376, filed on Jan. 20, 2005, theentire contents of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the vehicle monitoring method, thespecific character pattern recognition device, and the vehiclemonitoring system in which the specific character pattern of a vehicleis recognized and monitored.

2. Description of the Related Art

Specific character patterns are given to various kinds of vehiclesrespectively such that the patterns may not overlap. Therefore,performing automatic reading of the specific character pattern torecognize the specific character pattern of the vehicle is possible.

There have been proposed various kinds of systems that are applicable tothe automation of charge payment of the tollgates on the toll roads, thejudgment of whether the parking vehicles of the parking lot are thecontractors' own, and the detection of burglar vehicles or the like. Insuch systems, the image signal indicating the image of the vehiclespecific character pattern has to be processed. It is demanded for suchsystems to carry out the image processing of the image signalefficiently.

FIG. 7 shows the composition of the conventional vehicle monitoringdevice.

In the vehicle monitoring device of FIG. 7, the vehicle detecting unit70 detects that the passing vehicle arrives at the image-takingposition, and outputs the detection signal to the recognition processingunit 72. The recognition processing unit 72 outputs the image-takinginstruction to the image-taking unit 71 to take the image of the passingvehicle. The image-taking unit 71 takes the image of the vehicleaccording to the image-taking instruction, and transmits the resultingimage signal to both the recognition processing unit 72 and the imagetransmission unit 74.

The recognition processing unit 72 extracts the specific characterpattern area from the taken image of the vehicle, and recognizes thevehicle specific character pattern based on the characters or numbersincluded in the specific character pattern area. As for the recognitionprocessing of the vehicle specific character pattern, there are knownvarious kinds of means, such as means for clipping of one character,means for pattern matching of the clipped character, and means formatching through the feature extraction.

The vehicle monitoring device of FIG. 7 is configured so that, only whenthe passing vehicle passes through the image-taking position, theimage-taking unit 71 takes the image of the passing vehicle.

Moreover, the vehicle specific character patterns are registeredbeforehand in the matching unit 73. The vehicle specific characterpattern which is recognized by the recognition processing unit 72 istransmitted to the matching unit 73, and the matching unit 73 performsmatching of the received vehicle specific character pattern with therecorded vehicle specific character patterns. And the matching unit 73transmits the result of the matching to the recognition processing unit72.

If the signal indicating the matching coincidence is received from thematching unit 73, the recognition processing unit 72 transmits thematched vehicle specific character pattern to the image transmissionunit 74. The image transmission unit 74 transmits the vehicle specificcharacter pattern and the taken image signal to the imagerecording/displaying unit 75. The image recording/displaying unit 75adds the date information and the image-taking position information tothe received pattern/image information and records the resultinginformation. In the image recording/displaying unit 75, the recordedinformation is searched and read out based on the information related tothe vehicle specific character pattern, the date, the image-takingposition, etc., when the necessity occurs. The read-out information isdisplayed on the monitor of the image recording/displaying unit 75,which enables the checking of the vehicle of concern by viewing themonitor. See Japanese Laid-Open Patent Application No. 09-282590.

Moreover, there is known another vehicle monitoring method (see JapaneseLaid-Open Patent Application No. 09-261620). In this method, the vehiclespecific character pattern on the specific character pattern isrecognized based on the taken image signal, compression processing ofthe taken image signal is performed, and the recognized vehicle specificcharacter pattern is added to the compressed image signal so that theresulting image information is recorded. The compressed image signal ofthe recorded information is read out based on the vehicle specificcharacter pattern, and expansion processing (decompression processing)of the read compressed image signal is performed so that the expandedimage is displayed on the monitor.

Moreover, there is known another vehicle monitoring device (see JapaneseLaid-Open Patent Application No. 09-037232). In this device, a remotemonitoring unit is provided in which one monitoring range is selectedfrom among a plurality of monitoring ranges, the compression ratio ofthe image signal and the transmission time are changed corresponding tothe selected monitoring range, and the transmission of the compressedimage signal is performed.

For example, when the monitored object is moving at high speed in theselected monitoring range, the compression ratio is made high and thetransmission of the image signal is performed at high speed in order toallow the monitoring screen to follow the change of the monitored objectduring the high-speed movement. When the monitored object is moving atlow speed in the selected monitoring range, the compression ratio ismade low and the transmission of the image signal is performed at lowspeed in order to make the resolution of the monitoring screen high,increasing the quality of the image being displayed.

As mentioned above, the image of the vehicle specific character patternis taken, the specific character pattern is extracted from the takenimage signal through the image processing, and the character recognitionprocessing is performed, so that vehicle monitoring can be carried outbased on the recognized character pattern.

However, the image-taking conditions are greatly different depending onthe angle of attachment of the specific character pattern, the state ofthe dirt in the specific character pattern, and the weather condition.Therefore, in the case of a poor weather condition, it is difficult torecognize the specific character pattern through the image processing.

In the case where the recognition processing of the specific characterpattern of the vehicle is difficult to perform, an improved recognitionprocessing unit can be adopted to recognize the vehicle specificcharacter pattern. In the improved recognition processing unit, thetaken image signal is inputted to the display unit and the image of thevehicle is displayed on the display monitor. The area of the specificcharacter pattern in the image of the vehicle can be identified byviewing the image on the display monitor.

However, when the display monitor is installed at a position that isdistant from the installation position of the image transmission unit 74as shown in FIG. 7, it is necessary to transmit the image data from theimage transmission unit 74 to the monitor through the telephone line.Even if the compression processing of the image data is carried out,there is much amount of image data contained in one screen of the image,and the use of high-speed transmission path is required. Therefore, ithas been difficult to carry out the vehicle monitoring remotely byconnecting the center and the distributed image processing units throughthe existing communication network of low bit rate.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved vehiclemonitoring method in which the above-mentioned problems are eliminated.

Another object of the present invention is to provide a vehiclemonitoring method in which the compression range and compression ratiofor the compression processing of the taken image signal are controlledin response to the result of recognition processing of the specificcharacter pattern of the vehicle in order to reduce the amount of thetransmission data.

In order to achieve the above-mentioned objects, the present inventionprovides a vehicle monitoring method comprising the steps of: performingrecognition processing of a specific character pattern of a vehicle byextracting a specific character pattern area from a taken image data inorder to monitor the vehicle based on a recognized character pattern;setting, when a result of the recognition processing indicates that thespecific character pattern cannot be recognized, a compression range toa vehicle area containing the whole vehicle, clipped from the takenimage data, wherein image data of the clipped area is compressed at apredetermined low compression ratio to store or transmit the compressedimage data; setting, when the result indicates that the specificcharacter pattern is partially recognized, the compression range to thespecific character pattern area clipped from the taken image data,wherein image data of the clipped area is compressed at the lowcompression ratio to store or transmit the compressed image data; andsetting, when the result indicates that the specific character patternis fully recognized, the compression range to the specific characterpattern area clipped from the taken image data, wherein image data ofthe clipped area is compressed at a predetermined high compression ratioto store or transmit the compressed image data.

According to the present invention, when the vehicle specific characterpattern is fully recognized, the compressed image data in which theimage of the vehicle specific character pattern having the comparativelysmall area is compressed at the high compression ratio can betransmitted. It is possible to easily transmit the compressed image datathrough the communication network of low bit rate.

Moreover, in order to achieve the above-mentioned objects, the presentinvention provides a specific character pattern recognition devicecomprising: a recognition processing unit having a frame memory, acharacter recognition processing unit and an image processing unit, theframe memory temporarily storing an image data of a vehicle taken by animage-taking unit, the character recognition processing unit performingrecognition processing of a specific character pattern of the vehicle,and the image processing unit clipping a vehicle area containing thewhole vehicle from the taken image data and clipping a specificcharacter pattern area from the vehicle area; a compression range/ratiojudging unit judging a compression range and a compression ratio basedon a result of the recognition processing wherein, when the result ofthe recognition processing indicates that the specific character patterncannot be recognized, the compression range and the compression ratioare judged as being the vehicle area and a predetermined low compressionratio, when the result indicates that the specific character pattern ispartially recognized, the compression range and the compression ratioare judged as being the specific character pattern area and the lowcompression ratio, and when the result indicates that the specificcharacter pattern is fully recognized, the compression range and thecompression ratio are judged as being the specific character patternarea and a predetermined high compression ratio; an image compressionunit which is responsive to a judgment result of the compressionrange/ratio judging unit, the image compression unit clipping acorresponding area of image data for the compression range from thetaken image data of the frame memory, and performing compressionprocessing of the image data of the clipped area at the compressionratio; and a transmitting/receiving unit transmitting the compressedimage data from the image compression unit.

The above-mentioned specific character pattern recognition device may beconfigured so that the specific character pattern recognition devicefurther comprises a data storing unit which stores the compressed imagedata provided by the image compression unit, together with the result ofthe recognition processing of the specific character pattern of thevehicle.

Moreover, the above-mentioned specific character pattern recognitiondevice may be configured so that the specific character patternrecognition device further comprises a matching processing unit whichperforms matching processing between an externally requested vehiclespecific character pattern and the result of the recognition processingstored in the data storing unit, and, when a match occurs as a result ofthe matching processing, the compressed image data is read from the datastoring unit and transmitted.

Moreover, in order to achieve the above-mentioned objects, the presentinvention provides a vehicle monitoring system which includes aplurality of specific character pattern recognition devices and a centerwhich are connected through a communication line, each specificcharacter pattern recognition device comprising: a recognitionprocessing unit performing recognition processing of a specificcharacter pattern of a vehicle based on a taken image data, and therecognition processing unit clipping a vehicle area containing the wholevehicle from the taken image data, and clipping a specific characterpattern area from the vehicle area; a compression range/ratio judgingunit judging a compression range and a compression ratio based on aresult of the recognition processing wherein, when the result of therecognition processing indicates that the specific character patterncannot be recognized, the compression range and the compression ratioare judged as being the vehicle area and a predetermined low compressionratio, when the result indicates that the specific character pattern ispartially recognized, the compression range and the compression ratioare judged as being the specific character pattern area and the lowcompression ratio, and when the result indicates that the specificcharacter pattern is fully recognized, the compression range and thecompression ratio are judged as being the specific character patternarea and a predetermined high compression ratio; an image compressionunit which is responsive to a judgment result of the compressionrange/ratio judging unit, the image compression unit clipping acorresponding area of image data for the compression range from thetaken image data, and performing compression processing of the imagedata of the clipped area at the compression ratio; and atransmitting/receiving unit transmitting the compressed image data fromthe image compression unit, and the center comprising: a data managementtable in which the compressed image data received from each specificcharacter pattern recognition device through the communication line arestored; and a display unit displaying the compressed image data.

According to the present invention, the compression range andcompression ratio of the taken image data are determined in response tothe result of the automatic recognition processing of the vehiclespecific character pattern. Even when the vehicle specific characterpattern cannot be recognized, the compression processing of the vehiclearea, not the full screen, is performed, and the amount of thetransmission data can be reduced.

Moreover, the image data of the vehicle area can be displayed at thehigh compression ratio on the display unit at the center, thepossibility of recognition of the vehicle specific character pattern canbe increased by viewing the image with the high compression ratio on thedisplay unit. Moreover, when the vehicle specific character pattern canbe recognized, the compression processing of the specific characterpattern with the further smaller area is performed. Reducing the amountof the transmission data further is possible, and it is possible toeasily transmit the compressed image data through the communicationnetwork of low bit rate.

Since the ratio of recognition of the vehicle specific character patternis comparatively high, even when the compressed image data istransmitted continuously, the transmission data in many cases is thehighly compressed image data of the specific character pattern area. Theamount of the transmission data, even if it includes the data of therecognized vehicle specific character pattern, is comparatively small.It is possible to easily transmit the compressed image data through thecommunication network of low bit rate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

FIG. 1 is a diagram for explaining the outline composition of thevehicle monitoring system in the preferred embodiment of the invention.

FIG. 2 is a block diagram showing the composition of the vehiclemonitoring system in the preferred embodiment of the invention.

FIG. 3 is a flowchart for explaining the vehicle monitoring method inthe preferred embodiment of the invention.

FIG. 4 is a diagram for explaining the compression range.

FIG. 5 is a block diagram showing the composition of the vehiclemonitoring system in another preferred embodiment of the invention.

FIG. 6 is a block diagram showing the composition of the vehiclemonitoring system in another preferred embodiment of the invention.

FIG. 7 is a block diagram showing the composition of the conventionalvehicle monitoring system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A description will now be given of the preferred embodiments of thepresent invention with reference to the accompanying drawings.

FIG. 1 shows the outline composition of the vehicle monitoring system inthe preferred embodiment of the invention.

In FIG. 1, reference numeral 1 denotes the center, 2 denotes the controlprocessing unit, 3 denotes the display unit, 4 denotes the datamanagement table, 5 denotes the switched network (network), 6 denotesthe communication line, such as the telephone line, 7 denotes therecognition device, 8 denotes the camera, and 9 denotes the vehicle. Thevehicle monitoring system shown in FIG. 1 is constituted when theconnection between the center 1 and the recognition device 7 isestablished through the telephone line 6 which is accommodated in theswitched network 5. A plurality of recognition devices 7 whichconstitute part of the vehicle monitoring system may be distributed inthe highway, the general road or the parking lot, and each recognitiondevice 7 can be connected with the center 10 through the telephone line.

The camera 8 may be arranged at the position where the image of thevehicle running on the highway or the general road is taken, or at theposition where the image of the vehicle entering or exiting the parkinglot, or the image of the vehicle under parking is taken.

The recognition device 7 is provided with the image processing function,the character pattern recognition processing function, the datatransmitting/receiving function, etc. The recognition device 7 processesthe taken image data from the camera 8 by using the image processingfunction, and extracts the specific character pattern area of thevehicle 9 from the processed image data. The recognition device 7recognizes the vehicle specific character pattern by using the characterrecognition processing function. In response to the result of therecognition processing, the recognition device 7 clips the areacontaining the whole vehicle 9 or the specific character pattern areafrom the taken image data and determines the compression ratio. Therecognition device 7 transmits the resulting data (or the transmissiondata) to the center 1 through the telephone line 6 by using the datatransmitting/receiving function.

As shown in FIG. 1, the transmission data in this case comprises thespecific character pattern information and the compression image data.The compression image data contains, for example, the compression rangeindicating the vehicle area or the specific character pattern area, theimage quality, the compression data length, and the compressed imagedata. The specific character pattern information contains, for example,the header information, the position information, the time information,and the vehicle specific character pattern data with the recognitionresult, such as “12345”.

The control processing unit 2 of the center 1 is provided with the datamanagement table 4, and this data management table 4 stores thetransmission data received through the telephone line 6 from therecognition device 7. As shown in FIG. 1, the data management table 4contains, for every item, the vehicle specific character pattern whichis partially omitted, the image data in the compression range, the imagequality, and the position/time information.

In the data management table 4 of FIG. 1, for example, “12345” of thespecific character pattern column of the item number 1 indicates thecase in which the vehicle specific character pattern is fullyrecognized, the image data thereof indicates the specific characterpattern area (or the vehicle number plate region), and the image qualitythereof indicates the low level. Namely, the compression range is set tothe specific character pattern area, and the reproduction image qualityis set to the low level since the compression ratio has been set to thehigh compression ratio.

Moreover, in the data management table 4 of FIG. 1, “?” of the specificcharacter pattern column of the item number 3 indicates the case inwhich the vehicle specific character pattern cannot be recognized, theimage data thereof indicates the whole vehicle, and the image qualitythereof indicates the high level. Namely, the compression range is setto the vehicle area, and the reproduction image quality is set to thehigh level since the compression ratio has been set to the lowcompression ratio.

Moreover, in the data management table 4 of FIG. 1, “12?45” of thespecific character pattern column of the item number 4 indicates thecase in which the characters in the vehicle specific character patternare partially recognized except for the character “?”, the image datathereof indicates the specific character pattern area, and the imagequality thereof indicates the high level. Namely, the compression rangeis set to the specific character pattern area, and the reproductionimage quality is set to the high level since the compression ratio hasbeen set to the low compression ratio.

For example, the case in which the image data of the item number 3 inthe data management table 4 is read and displayed on the display unit 3under control of the control processing unit 2 is considered. In thiscase, the compressed image data of the vehicle area has been created atthe low compression ratio, and such image data is decompressed anddisplayed. Thus, the image of the vehicle area can be displayed at thehigh reproduction image quality.

Accordingly, in this case, the specific character pattern area ischecked by viewing the display screen, and this makes it possible toread the characters in the specific character pattern area by viewing.In such case, the column of the specific character pattern in the datamanagement table 4 can be corrected to the vehicle specific characterpattern currently checked by viewing.

In the vehicle monitoring system of the present embodiment, thecompression processing of the vehicle area only is carried out, and theamount of the transmission data can be reduced as compared with the casein which the compression processing of the full screen is carried out.

Moreover, when the image data of the item number 4 in the datamanagement table 4 is read and displayed on the display unit 3 undercontrol of the control processing unit 2, the image of the specificcharacter pattern area can be displayed at the high image quality level.This make it possible to easily check the character “?” which has notbeen recognized through the automatic recognition processing by viewingthe display screen.

In such case, the column of the specific character pattern in the datamanagement table 4 can also be corrected to the vehicle specificcharacter pattern currently checked by viewing. In the vehiclemonitoring system of the present embodiment, the compression processingof the specific character pattern area only is carried out, and theamount of the transmission data can be reduced further as compared withthe case in which the compression processing of the full screen or thevehicle area is carried out.

In the case in which the vehicle specific character pattern is fullyrecognized through the automatic recognition like the item number 1, 2or 6 in the data management table 4, the compression processing of thespecific character pattern area is performed at the high compressionratio (which allows the reproduction image quality to be set to the lowlevel), and the amount of the transmission data can be reduced further.

In such case, when the vehicle specific character pattern which isalready recognized through the automatic recognition is displayed on thedisplay unit 3, checking the vehicle specific character pattern againcan be easily performed even if the reproduction image quality is at thelow level.

FIG. 2 shows the composition of the vehicle monitoring system in thepreferred embodiment of the invention.

In FIG. 2, reference numeral 10 denotes the center, 11 denotes thetransmitting/receiving unit, 12 denotes the control processing unit, 13denotes the display unit, 14 denotes the data management table, 20denotes the specific character pattern recognition device, 21 denotesthe recognition processing unit, 22 denotes the frame memory, 23 denotesthe compression range/ratio judging unit, 24 denotes the imagecompression unit, 25 denotes the transmitting/receiving unit, 30 denotesthe image-taking unit, and 40 denotes the telephone line.

The center 10 is equivalent to the center 1 in FIG. 1, the specificcharacter pattern recognition device 20 is equivalent to the recognitiondevice 7 in FIG. 1, the image-taking unit 30 is equivalent to the camera8 in FIG. 1, and the telephone line 40 is equivalent to the telephoneline 6 in FIG. 1.

Moreover, the control processing unit 12 corresponds to the controlprocessing unit 2 in FIG. 1, the display unit 13 corresponds to thedisplay unit 3 in FIG. 1, and the data management table 14 is equivalentto the data management table 4 in FIG. 1. In addition, in thecomposition of FIG. 2, the network 5 in FIG. 1 is omitted for the sakeof convenience of illustration.

In the vehicle monitoring system of FIG. 2, the image-taking unit 30continuously takes at a predetermined frame period the image of thevehicle passing position or parking position which is selected as theimage-taking range, similar to a television camera. Alternatively, theimage-taking unit 30 may be configured so that it takes the image of thevehicle only when the vehicle exists within the image-taking range.

In the specific character pattern recognition device 20, the taken imagesignal received from the image-taking unit 30 is digitized by therecognition processing unit 21, and stored into the frame memory 22 ofthe recognition processing unit 21.

In the case in which the image is taken continuously, the recognitionprocessing unit 21 can recognize the difference between the backgroundportion (such as the road) and the moving-vehicle portion of the takenimage by taking the difference between the frames at the predeterminedtime interval. Thus, the recognition processing unit 21 clips thevehicle area containing the vehicle, from the taken image.

Further, the recognition processing unit 21 clips the specific characterpattern area (e.g., the vehicle number plate) from the vehicle area, andperforms the character recognition processing to recognize thecharacters or numbers in the specific character pattern area.

The compression range/ratio judging unit 23 controls the compressionrange and the compression ratio in response to the result of therecognition processing of the vehicle specific character patternreceived from the recognition processing unit 21.

As mentioned above, the compression range/ratio judging unit 23 performsthe judgment about the compression range and the compression ratio asfollows. When the vehicle specific character pattern cannot berecognized, the compression range is determined as being the vehiclearea, and the compression ratio is determined as being the predeterminedlow compression ratio. Moreover, when the vehicle specific characterpattern is fully recognized, the compression range is determined asbeing the specific character pattern area, and the compression ratio isdetermined as being the predetermined high compression ratio.Furthermore, when the vehicle specific character pattern is partiallyrecognized but the remainder cannot be recognized, the compression rangeis determined as being the specific character pattern area, and thecompression ratio is determined as being the predetermined lowcompression ratio.

The image compression unit 24 performs clipping and compressionprocessing of the area of the image data of the frame memory 22according to the judgment signal from the compression range/ratiojudging unit 23. The image compression unit 24 transmits the compressedimage data to the transmitting/receiving unit 25 through the compressionrange/ratio judging unit 23, or transmits the compressed image data tothe transmitting/receiving unit 25 directly. The transmitting/receivingunit 25 transmits the compressed image data from the specific characterpattern recognition device 20 to the center 10 through the telephoneline 40.

The center 10 temporarily stores in the data management table 14 thecompression image data received at the transmitting/receiving unit 11under control of the control processing unit 12.

The control processing unit 12 reads the compressed image data of thevehicle with which the vehicle specific character pattern cannot berecognized through the automatic recognition processing, from the datamanagement table 14 automatically or in response to the instructions ofthe operator. The compressed image data is subjected to the expansionprocessing in accordance with the compression ratio specified therein,and the expanded image data is displayed on the display unit 13.

In this case, since the image of the vehicle area can be displayed atthe high image-quality level, it is possible to increase the possibilitythat the vehicle specific character pattern be visually recognized byviewing the display screen.

FIG. 3 is a flowchart for explaining the vehicle monitoring method inthe preferred embodiment of the invention.

As shown in FIG. 3, the taken image signal received from theimage-taking unit 30 (see FIG. 2) is digitized and stored in the framememory 22 (S1). The difference data (the outline of the vehicle) betweenthe background image data and the taken image data is extracted (S2).

The difference data extracted at the step S2 takes the differencebetween the frames at the predetermined time interval and indicates thedifference between the background portion (such as the road) and themoving-vehicle portion of the taken image. The vehicle area containingthe vehicle is clipped from the taken image data using the differencedata (S3).

And it is determined whether the vehicle can be recognized or not (S4).Vehicles generally have various kinds of form, but they have the sizeand the form different from the pedestrian etc. Thus, the vehicles andthe other moving objects are distinguishable.

When the vehicle cannot be recognized using the difference data, thecontrol is transferred to the step S1. On the other hand, when thevehicle has been recognized, the control is transferred to the next stepS5.

In the step S5, extraction processing of the specific character patternarea from the clipped area is performed. For example, the histogram withrespect to the horizontal direction and the vertical direction can becreated, and the area of the rectangular specific character pattern canbe extracted based on this histogram.

Alternatively, for example, the background color of the specificcharacter pattern is set to white, and the generally rectangle areawhere the color of the background other than the characters is white canbe extracted as the specific character pattern area.

Next, it is determined whether the specific character pattern has beenrecognized (S6). When the result at the step S6 is affirmative, thecharacter area is clipped and the numeric values of the characters ofthe specific character pattern are determined by the pattern matching(S7). Namely, the character recognition is performed for the clippedcharacter area through the pattern matching, the feature pointextraction, etc.

Next, it is determined whether all the characters in the specificcharacter pattern area have been recognized, or it is determined whetherthe vehicle specific character pattern has been fully recognized (S8).

When the result at the step S8 is affirmative, the image data of thevehicle specific character pattern area (which is the clipped area) iscompressed at the high compression ratio (which is specified as thecompression ratio in this case) (S9).

When the result at the step S8 is negative (i.e., when the vehiclespecific character pattern has been recognized partially), only thecharacters in the specific character pattern which have been recognizedare determined (S12). And the image data of the vehicle specificcharacter pattern area (which is the clipped area) is compressed at thelow compression ratio (which is specified as the compression ratio inthis case) (S13).

On the other hand, when the specific character pattern cannot berecognized, or when the vehicle specific character pattern has not beenrecognized at all, the image data of the vehicle area (which is theclipped area) is compressed at the low compression ratio (which isspecified as the compression ratio in this case) (S11).

Subsequently, the transmission data as shown in FIG. 1 is created, andthe compressed image data with the specific character pattern istransmitted from the specific character pattern recognition device 20 tothe center 10 (S10).

FIG. 4 is the diagram for explaining the compression range. In FIG. 4,(a) indicates the taken image created by the image-taking unit 30 (seeFIG. 2). For example, the image data stored in the frame memory 22 isread out and displayed on the display screen.

And when the extraction of the specific character pattern cannot beperformed, or when the automatic recognition of the vehicle specificcharacter pattern cannot be performed at all, the vehicle area isclipped from the taken image data as shown by (b) in FIG. 4. The imagedata of the vehicle area is compressed at the low compression ratio bythe image compression unit 24, allowing the image quality to be set atthe high level.

Therefore, when the compressed image data in this case is received atthe center 10, the image data is expanded and displayed on the displayunit 13. In this case, the image of the vehicle with the high imagequality level can be displayed, and the specific character pattern areacan be checked by viewing the display screen, which increases thepossibility that the vehicle specific character pattern be recognized byviewing.

Moreover, when the vehicle specific character pattern is partiallyrecognized through the automatic recognition, the image data of thespecific character pattern area is compressed at the low compressionratio.

Therefore, the specific character pattern area is clipped from the takenimage data as shown by (c) or (d) in FIG. 4, and, when the compressedimage data of the specific character pattern area with the lowcompression ratio is received at the center 10, the image data isexpanded and displayed on the display unit 13. In this case, the imageof the specific character pattern area with the high image quality levelcan be displayed, and the specific character pattern area can be checkedby viewing the display screen, which increases the possibility that thevehicle specific character pattern be fully recognized by viewing.

Next, FIG. 5 shows the composition of the vehicle monitoring system inanother preferred embodiment of the invention.

In FIG. 5, the elements which are the same as corresponding elements inFIG. 2 are designated by the same reference numerals, and a descriptionthereof will be omitted.

In the specific character pattern recognition device 20 of FIG. 5, thedata storing unit 26 is provided. This data storing unit 26 is formed bya semiconductor integrated circuit memory or a hard disk drive unitwhich is provided to accumulate the image data. The data storing unit 26is provided to accumulate the image data, and to accumulate thecompression data of the image compression unit 24, the recognitionresult of the vehicle specific character pattern by the recognitionprocessing unit 21, and the judgment result of the compressionrange/ratio judging unit 23.

For example, the compression data are accumulated in the data storingunit 26 in the format equivalent to the format of the data managementtable 4 or the format of the transmission data shown in FIG. 1.

And the data storing unit 26 is searched from the center 10 inaccordance with the time specified by the center 10 or in accordancewith the vehicle specific character pattern specified by the center 10.The compression data which is retrieved and extracted is read out fromthe data storing unit 26. The compression data is transmitted from thetransmitting/receiving unit 25 to the telephone line 40 in the format ofthe transmission data (which is, for example, shown in FIG. 1).

Therefore, it is possible for the present embodiment that, only when thenecessity occurs in the center 10, the automatically recognized vehiclespecific character pattern and the compression image data be collectedfrom the specific character pattern recognition device 20.

FIG. 6 shows the composition of the vehicle monitoring system in anotherpreferred embodiment of the invention.

In FIG. 6, the elements which are the same as corresponding elements inFIG. 2 or FIG. 5 are designated by the same reference numerals, and adescription thereof will be omitted.

In the specific character pattern recognition device 20 of FIG. 6, thematching processing unit 27 is provided. When the vehicle specificcharacter pattern is specified by the center 10, the matching processingunit 27 searches the vehicle specific character pattern stored in thedata storing unit 26, and carries out matching between the specifiedvehicle specific character pattern and the recognized vehicle specificcharacter pattern. If the coincidence of the matching occurs, thecompression image is read from the data storing unit 26, and thetransmission data in the format shown in FIG. 1 is transmitted from thetransmitting/receiving unit 25 to the center 10 through the telephoneline 6.

The present invention is not limited to the above-described embodiments,and variations and modifications may be made without departing from thescope of the present invention. For example, the camera 8 or theimage-taking unit 30 may be constituted by a digital camera, so that theimage of the vehicle is taken using the digital camera at intervals of afixed time period. Moreover, two frame memories 22 may be provided inorder to perform the processing of creating the difference data moreeasily. Moreover, the vehicle monitoring system may be controlled tochange the compression ratio to one of the multiple stages correspondingto the number in which the vehicle specific character pattern isrecognized.

1. A vehicle monitoring method comprising the steps of: performingrecognition processing of a specific character pattern of a vehicle byextracting a specific character pattern area from a taken image data inorder to monitor the vehicle based on a recognized character pattern;determining, when a result of the recognition processing indicates thatthe specific character pattern cannot be recognized, a compression rangeas being a vehicle area clipped from the taken image data, wherein imagedata of the clipped area is compressed at a predetermined lowcompression ratio to store or transmit the compressed image data;determining, when the result indicates that the specific characterpattern is partially recognized, the compression range as being thespecific character pattern area clipped from the taken image data,wherein image data of the clipped area is compressed at the lowcompression ratio to store or transmit the compressed image data; anddetermining, when the result indicates that the specific characterpattern is fully recognized, the compression range as being the specificcharacter pattern area from the taken image data, wherein image data ofthe clipped area is compressed at a predetermined high compression ratioto store or transmit the compressed image data.
 2. A specific characterpattern recognition device comprising: a recognition processing unithaving a frame memory, a character recognition processing unit and animage processing unit, the frame memory temporarily storing an imagedata of a vehicle taken by an image-taking unit, the characterrecognition processing unit performing recognition processing of aspecific character pattern of the vehicle, and the image processing unitclipping a vehicle area containing the whole vehicle from the takenimage data and clipping a specific character pattern area from thevehicle area; a compression range/ratio judging unit judging acompression range and a compression ratio based on a result of therecognition processing wherein, when the result of the recognitionprocessing indicates that the specific character pattern cannot berecognized, the compression range and the compression ratio are judgedas being the vehicle area and a predetermined low compression ratio,when the result indicates that the specific character pattern ispartially recognized, the compression range and the compression ratioare judged as being the specific character pattern area and the lowcompression ratio, and when the result indicates that the specificcharacter pattern is fully recognized, the compression range and thecompression ratio are judged as being the specific character patternarea and a predetermined high compression ratio; an image compressionunit which is responsive to a judgment result of the compressionrange/ratio judging unit, the image compression unit clipping acorresponding area of image data for the compression range from thetaken image data of the frame memory, and performing compressionprocessing of the image data of the clipped area at the compressionratio; and a transmitting/receiving unit transmitting the compressedimage data from the image compression unit.
 3. The specific characterpattern recognition device according to claim 2 further comprising adata storing unit storing the compressed image data provided by theimage compression unit, together with the result of the recognitionprocessing of the specific character pattern of the vehicle.
 4. Thespecific character pattern recognition device according to claim 3further comprising a matching processing unit performing matchingprocessing between an externally requested vehicle specific characterpattern and the result of the recognition processing stored in the datastoring unit, and, when a match occurs as a result of the matchingprocessing, the compressed image data is read from the data storing unitand transmitted.
 5. A vehicle monitoring system including a plurality ofspecific character pattern recognition devices and a center which areconnected through a communication line, each specific character patternrecognition device comprising: a recognition processing unit performingrecognition processing of a specific character pattern of a vehiclebased on a taken image data, and the recognition processing unitclipping a vehicle area containing the whole vehicle from the takenimage data, and clipping a specific character pattern area from thevehicle area; a compression range/ratio judging unit judging acompression range and a compression ratio based on a result of therecognition processing wherein, when the result of the recognitionprocessing indicates that the specific character pattern cannot berecognized, the compression range and the compression ratio are judgedas being the vehicle area and a predetermined low compression ratio,when the result indicates that the specific character pattern ispartially recognized, the compression range and the compression ratioare judged as being the specific character pattern area and the lowcompression ratio, and when the result indicates that the specificcharacter pattern is fully recognized, the compression range and thecompression ratio are judged as being the specific character patternarea and a predetermined high compression ratio; an image compressionunit which is responsive to a judgment result of the compressionrange/ratio judging unit, the image compression unit clipping acorresponding area of image data for the compression range from thetaken image data, and performing compression processing of the imagedata of the clipped area at the compression ratio; and atransmitting/receiving unit transmitting the compressed image data fromthe image compression unit, and the center comprising: a data managementtable in which the compressed image data received from each specificcharacter pattern recognition device through the communication line arestored; and a display unit displaying the compressed image data.